Lung Volumes

Question 1

What are the indications for measuring lung volumes?

Answer 1

Differentiate between obstructive vs restrictive
Assess response to therapy
Aid in the interpretation of other lung function tests
Determine severity of disease

Question 2

What are the 4 lung volumes?

Answer 2

IRV, ERV, Vt, RV

Question 3

Define lung capacities and name them

Answer 3

Consist of two or more lung volumes together

FRC, TLC, IC, VC

Question 4

What is the definition of a VC or SVC?

Answer 4

Maximum volume of air that can be exhaled from a maximum inhalation or vice versa
SVC=FRC (normally or withing 150 mls)

Question 5

what are the two techniques for performing a SVC?

Answer 5

Maximum inhalation followed by a maximum exhalation (most common) (VCex)
Maximum exhalation followed by a maximum inhalation (VCin)

Question 6

What biological factors influence VC?

Answer 6

Height, age, gender, race

Question 7

What is the definition of Tidal Volume (Vt)?

Answer 7

Volume of of inhaled and exhaled with each breath

stays relatively normal (5-7ml/kg) regardless of any disease

Question 8

What is the definition of an inspiratory capacity (IC)?

Answer 8

LArgest volume of air that can be inhaled from a resting exhalation

Question 9

What is the definition of Expiratory Reserve Volume (ERV)?

Answer 9

The volume of gas that can be normally exhaled from a normal expiratory baseline
May be slightly reduced with obesity or neuromuscular problems

Question 10

What is the definition of Functional Residual Capacity (FRC)?

Answer 10

The volume of gas remaining in the lungs at the end of normal expiration
FRC=End Expiratory Lung Volume (EELV)

Question 11

What are the two techniques for measuring FRC?

Answer 11

1. Plethysmography

2. Gas dilution methods: He dilution or N2 washout

Question 12

Describe a pressure box

Answer 12

Constant volume box
Box is closed to atmosphere
Functions on Boyle’s law
Changes in box pressure/volume reflect Palv changes and Vthorax changes

Question 13

Describe a flow box

Answer 13

Constant pressure box
Open to atmosphere
Flow is converted to volume
Pneumotach needs to be very sensitive to measure small flow changes

Question 14

What are the uses of Body Plethysmographs?

Answer 14

Measure FRCpl, Raw, Cl and static lung volumes and spirometry
Flow measured via pressure differential pneumotach
Pbox and Pmouth via pressure transducers
Shutter attached to pneumotach occlude airway at FRC and measure Palv

Question 15

What is Boyle’s law?

Answer 15

Volume of gas at a constant temperature varies inversely to the pressure applied to it
P1V1=P2V2

Question 16

Describe the He dilution method

Answer 16

Known as closed circuit method
Easy for the patient to perform (requires only tidal breathing)
instruments used are simple and inexpensive
C1V1=C2V2
Patients FRC dilutes initial He concentration to a new concentration
The change in He concentration is directly proportional to the patients FRC

Question 17

Describe the nitrogen washout method

Answer 17

Known as open circuit FRC method
Volume of N2 in the lungs start = volume of N2 in the spirometer at end
Patient breaths in 100% O2 to washout N2 (until less than 1.5% N2 in alveoli)
Totla volume of gas exhaled is measured and % of N2 in exhaled gas is measured

Question 18

What happens to FRC in obstructive disorders?

Answer 18

FRC is greater than 120% and RV is greater than 120%

Also decreased flowrates

Question 19

What happens to FRC in restrictive disorders?

Answer 19

FRC is decreased except in neuromuscular disorders

Question 20

What is the definition of Residual Volume (RV)?

Answer 20

The volume in the lungs at the end of maximum exhalation

It is calculated once the FRC has been determined (increased RV means an increased work of breathing)

Question 21

What can cause in increase in RV?

Answer 21

small airway obstruction
loss of elastic recoil
Loss of diaphragm function
loss of expiratory muscle force

Question 22

What is the definition of Total Lung Capacity (TLC)?

Answer 22

Total volume in the lungs at the end of a maximal inspiration
Calculated value
Can me measured via CXR, MRI or CT

Question 23

What is the significance of TLC?

Answer 23

Greater than 120% + other signs of obstruction = hyperinfaltion
Less than 120% + other signs of obstruction = airtrapping
Less than 80% = restrictive process

Question 24

Describe RV/TLC%

Answer 24

Describes the % of TLC that must be ventilated by tidal breathing
Normal RV/TLC% = 20-35%
(Restrictive = less than 20, obstructive = increased value)